Process control systems are widely used in factories and/or plants in which products are manufactured or processes are controlled (e.g., chemical manufacturing, power plant control, etc.) Process control systems are also used in the harvesting of natural resources such as, for example, oil and gas drilling and handling processes, etc. Virtually any manufacturing process, resource harvesting process, etc. can be automated through the application of one or more process control systems.
The manner in which process control systems are implemented has evolved over the years. Older generations of process control systems were typically implemented using dedicated, centralized hardware. However, modern process control systems are typically implemented using a highly distributed network of workstations, intelligent controllers, smart field devices, and the like, some or all of which may perform a portion of an overall process control strategy or scheme. In particular, most modern process control systems include smart field devices and other process control components that are communicatively coupled to each other and/or to one or more controllers via one or more digital data busses. Of course, many of these modern process control systems may also include non-smart field devices such as, for example, 4-20 milliamp (MA) devices, 0-10 volts direct current (VDC) devices, etc., which are typically directly coupled to controllers as opposed to a shared digital data bus or the like.
In any event, field devices include, for example, input devices (e.g., devices such as sensors that provide status signals that are indicative of process control parameters such as, for example, temperature, pressure, flow rate, etc.), as well as control operators or actuators that perform actions in response to commands received from controllers and/or other field devices. For example, a controller may send signals to a valve to increase pressure or flow, to a heater or chiller to change a temperature, to a mixer to agitate ingredients in a process control system, etc.
One particularly important aspect of process control system design involves the manner in which field devices are communicatively coupled to each other, controllers and other systems or devices within a process control system. In general, the various communication channels, links and paths that enable the field devices to function within the process control system are commonly collectively referred to as an input/output (I/O) communication network.
The communication network topology and physical connections or paths used to implement an I/O communication network can have a substantial impact on the robustness or integrity of field device communications, particularly when the I/O communications network is subjected to environmental factors or conditions associated with the process control system. For example, many industrial control applications often subject field devices and their associated I/O communication networks to harsh physical environments (e.g., high, low or highly variable ambient temperatures, vibrations, corrosive gases or liquids, etc.), difficult electrical environments (e.g., high noise environments, poor power quality, transient voltages, etc.), etc. In any case, environmental factors can compromise the integrity of communications between one or more field devices, controllers, etc. In some cases, such compromised communications could prevent the process control system from carrying out its control routines in an effective or proper manner, which could result in reduced process control system efficiency and/or profitability, excessive wear or damage to equipment, dangerous conditions that could damage or destroy equipment, building structures and/or people, etc.
Historically, the I/O communication networks used in process control systems have been hardwired networks. In particular, the field devices within these process control systems have typically been communicatively coupled to controllers, workstations, and other process control system components using a hierarchical topology in which non-smart field devices are directly coupled to controllers using analog interfaces such as, for example, 4-20 mA, 0-10 VDC, etc. In many cases, smart field devices are also used and are coupled via hardwired digital data busses, which are coupled to controllers via smart field device interface devices.
While hardwired I/O communication networks can initially provide a robust I/O communication network, their robustness can be seriously degraded over time as a result of environmental stresses (e.g., corrosive gases or liquids, vibration, humidity, etc.). For example, contact resistances associated with the I/O communication network wiring may increase substantially due to corrosion, oxidation and the like. In addition, wiring insulation and/or shielding may degrade or fail, thereby creating a condition under which environmental electrical interference or noise can more easily corrupt the signals transmitted via the I/O communication network wires. In some cases, failed insulation may result in a short circuit condition that results in a complete failure of the associated I/O communication wires.
Additionally, hardwired I/O communication networks are typically expensive to install, particularly in cases where the I/O communication network is associated with a large industrial plant or facility that is distributed over a relatively large geographic area. In many instances, the wiring associated with the I/O communication network may have to span relatively long distances and/or through, under or around many structures (e.g., walls, buildings, equipment, etc.) Such long wiring runs typically involve substantial amounts of labor and, thus, expense. Further, such long wiring runs are especially susceptible to signal degradation due to wiring impedances and coupled electrical interference, both of which can result in unreliable communications.
Hardwired I/O communication networks are also typically very difficult to reconfigure. For example, adding a new field device typically requires the installation of wires between the new field device and a controller. Retrofitting a field device in this manner may be very difficult and expensive due to the long wiring runs and space constraints that are often found in older process control plants and/or systems. For example, high wire counts within conduits, equipment and/or structures interposing along available wiring paths, etc., may significantly increase the difficulty associated with retrofitting field devices to an existing system. Similarly, changing an existing field device with a new device having different field wiring requirements may present the same difficulties in the case where more and/or different wires have to be installed to accommodate the new device.
Wireless I/O communication networks are often used to alleviate some of the difficulties associated with hardwired I/O networks. However, most, if not all, wireless I/O communication networks are implemented using relatively expensive hardware devices (e.g., wireless enabled routers, hubs, switches, etc.), most of which consume a relatively large amount of power. In addition, known wireless I/O communication networks, including the hardware and software associated therewith, use point-to-point communication paths that are carefully selected during installation and fixed during subsequent operation of the system. Establishing the fixed communication paths within these known wireless I/O communication networks typically involves the use of one or more experts to perform an expensive site survey that enables the experts to determine the types and/or locations of the transceivers and other communication equipment. Further, once the fixed point-to-point communication paths have been selected via the site survey results, one or more of the experts must then configure equipment, tune antennas, etc.
While known wireless I/O communication networks can, for example, alleviate the long term robustness issues associated with hardwired communication paths, these known wireless I/O communication networks are relatively inflexible. Specifically, because point-to-point communication paths are used, retrofitting one or more additional or different field devices to an established wireless I/O communication network may require relatively extensive reconfiguration of the existing communication paths to accommodate a new or changed communication path. Further, adding or changing a communication path may require the services of one or more experts to develop a new or revised site survey and to configure or reconfigure equipment, antennas, etc. to accommodate the additional or different field devices. Thus, due to the costs associated with installing a wireless I/O communication network (e.g., site surveys, expert configuration, etc.), wireless I/O communication networks are often cost prohibitive, particularly for relatively large process control systems such as those typically used in industrial applications.
A further difficulty with most, if not all, hardwired and wireless I/O communication networks is that the physical locations and connections associated with the field devices in systems employing such networks are dependent on the logical control strategy. In other words, the logical control strategy is developed to associate particular field devices with particular communication paths and physical locations throughout the process control system. As a result, changing the location of a field device and/or the communication path(s) coupling that communication device to a controller implementing at least a part of the overall control strategy (which uses that field device) typically requires corresponding changes to the control strategy. Such changes to the control strategy may involve time consuming, and, thus, expensive effort by a system operator or other user via one or more system workstations.
Likewise, replacement of a damaged or failing field device is a relatively time consuming process with existing hardwired and wireless I/O communication networks. For example, when a field device (e.g., a valve, a temperature sensor, etc.) fails or is failing in the field, maintenance personnel typically replace the field device. However, before such a replacement may be made, a replacement device must be programmed, which includes storing a unique identifier used by the failing or failed field device in the replacement field device. This programming is not typically performed in the field, but is usually carried out by maintenance personnel at a central station. Subsequent to programming at the central station, the replacement device is taken into the field and installed. In situations where multiple field devices are distributed across a wide geographical area, programming replacement components at a central station is time consuming because multiple trips from the field to the central station may be required, depending upon when maintenance personnel become aware of a need to replace the field devices.
In addition to unique identifiers, smart field devices also typically store other data and/or routines. Accordingly, in addition to programming replacement devices with the appropriate unique identifier, replacement devices must also be programmed with the latest versions of processes or routines stored in the failed devices at the time of their removal.
As will be readily appreciated from the foregoing, programming replacement field devices with unique identifiers, processes, routines and/or other process control data can be very cumbersome, especially in situations in which the field devices are distributed across wide geographical areas. Additionally, while the foregoing has described problems associated with replacing field device components, those having ordinary skill in the art will readily recognize that components other than field devices within a process control system are also cumbersome to replace. For example, the replacement of controllers, input/output (I/O) devices (wireless or wired), communications hubs, etc. also requires significant reprogramming effort. Accordingly, the replacement of any process control component or device and the reprogramming associated therewith can prove very time consuming and expensive.